A new highly-effective class of low molecular weight brominated aromatic polymer compositions has recently been discovered in our laboratories. These compositions have the formula:C6H(5-x)BrxCH2CH2(C6H(5-x)BrxCHCH2—)nCH2C6H(5-x)Brx wherein n is an average number in the range of about 2.9 to about 3.9, wherein each x is the same or different and is a whole number in the range of 3 to 5, the average number of all of the x's in the composition being in the range of about 3.50 to about 3.80 and the weight percent of bromine as determined by X-Ray Fluorescence Spectroscopy (XRF) in the polymer being in the range of about 73.4 to about 74.5. A detailed description of these new brominated aromatic polymer compositions and their preparation and uses is presented in commonly-owned Provisional U.S. Patent Application No. 61/119,289, filed Dec. 2, 2008, all disclosure of which is incorporated herein by reference.
Because of the relatively low molecular weights of the polymers of the above formula (e.g., an Mw in the range of about 3000), it would not be expected that the above low molecular weight brominated aromatic polymer compositions would have sufficient intrinsic strength to be directly converted into pellets without co-formation of considerable amounts of powdery co-product, including powders in the form of dusts. Dust and powder formation is of course very undesirable, especially if the dusts become entrained in the air. Moreover, unless the dusts and powders are recovered for recycle, their formation would result in loss of desirable product and consequent economic loss.
The expectation that the above relatively low molecular weight polymers would not be expected to have sufficient intrinsic strength to be directly converted into pellets without co-formation of considerable amounts of powdery co-product, including powders in the form of dusts is based on actual experience in our laboratories. As pointed out in commonly-owned WO 2008/011477, anionic styrenic polymers such as anionic polystyrene, a polystyrene formed by use of an anionic polymerization inhibitor system, have “a propensity to form substantial amounts of small particles and powders when attempts are made to pelletize the product. It appears that the pellets, unless bound together by an extraneous binding agent or the like, tend during formation, handling, and/or packaging to break apart and to revert to small particles and finely-divided powder, typically referred to as “fines”. Because of this characteristic, various conventional pelletizing or compacting procedures are unsuitable for producing brominated anionic styrenic polymers essentially free of fines and that during shipment and handling remain essentially free of fines. As can be readily appreciated, the existence or formation of fines in a product of this type is not only detrimental to the appearance of the pelletized product but in addition is undesired by the consumer.”
In as much as the foregoing quotation applies to a type of polymer having molecular weights (Mw) typically in the region of about 13,000, it can be seen that with a polymer having an Mw in the region of about 3000, the expectation would be that useful pellets could not be made without a binder and even if a binder were used, the amount of such binder in a pelletized product would necessarily be relatively high in order to keep the amount of fines and dust particles to a satisfactory minimum.
Indeed, it would be of considerable advantage if a way could be found of converting powdery polymers of the type referred to above into pellets which, even if susceptible to breakup during handling or use, would form smaller aggregates with little, if any, co-formation of air-entrainable dusts.